Both vertical and planar (or horizontal) Hall effect elements are known types of semiconductor elements that can be used to sense and external magnetic field. The vertical and the planar Hall effect elements have different semiconductor structures.
A vertical Hall effect element has an axis of maximum sensitivity parallel to a major surface of a substrate upon which the vertical Hall elements is formed. In contrast, a planar Hall effect element has an axis of maximum sensitivity perpendicular to a major surface of a substrate upon which the planar Hall elements is formed.
A conventional planar Hall effect element is a four terminal device, the four terminals coupled to a Hall plate. The Hall effect element can also include a field plate disposed over the Hall plate. Two of the terminals can be configured to pass a current between the two terminals and the other two terminals can provide a voltage in response to a magnetic field. The Hall plate can be comprised of a first portion of an N-type epitaxial layer disposed over a P-type substrate. The field plate can he comprised of a portion of a metal layer disposed over the Hall plate.
From the description above, it should be apparent that there can be a P/N junction (a diode) from the P-type substrate to another portion of the N-type epitaxial layer, for example, the another portion of the N-type epitaxial layer of an output circuit. The P/N junction can be subject to undesirable minority carrier charge flowing from the P-type substrate into the another portion of the N-type epitaxial layer when there is a sufficient voltage (e.g., 0.7 volts) between the P-type substrate and the N-type epitaxial layer. The sufficient voltage could be generated as a result of external electro-magnetic interference (EMI), for example, radio waves.
In the presence of the above minority carrier flow, the Hall plate formed with the first portion of the N-type epitaxial layer can act as a collector of a transistor. Other portions of the N-type epitaxial layer can also act as collectors, but the first portion of the N-type epitaxial layer of the Hall plate may be particularly susceptible. Thus, the minority carrier charge flow can cause unintended and undesirable effects on the function of the circuit, e.g., magnetic field sensor, when exposed to EMI.
It would be desirable have a planar Hall effect element for which charge is not able to flow the from the P-type substrate to the N-type Hall plate when the circuit, e.g., magnetic field sensor, is subject to EMI.